"The Guarded Secret of the Plants": Will Dan Nocera's Artificial Leaf Revolutionize Energy?0

Rachel Nuwer | Tue May 15 2012

In 1912, ten years before his death, Giacomo Luigi Ciamician predicted the world’s clean energy future. “On the arid lands there will spring up industrial colonies without smoke and without smokestacks; Forests of glass tubes will extend over the plains and glass buildings will rise everywhere,” Ciamician, a nine-time Nobel prize nominee, declared. Within that glass world, he asserted, “will take place the photochemical processes that hitherto have been the guarded secret of the plants.” Even if the coalmines were emptied, civilization would prosper so long as the sun shined.

A hundred years later, Ciamician’s apostles, chief among them Daniel Nocera, are still pursuing the “guarded secret of the plants.” Nocera, who is the Henry Dreyfus Professor of Energy at the Massachusetts Institute of Technology, is working to realize that long-ago dream of capturing “the guarded secret of the plants.” He has built an artificial leaf.

Photosynthesis “is how the whole world operates,” he said. “We’ve been operating like that for 2.5 billion years, and we’ll probably keep on operating like that.”

When dropped into a jar of water exposed to sunlight, the leaf bubbles like a tablet of Alka-Seltzer.

Nocera’s leaf, which he described in American Chemical Society’s journal Accounts of Chemical Research, is designed to capture the solar energy of the sun. It plays upon the underpinning principle of green plants’ photosynthesis, which splits water molecules to capture energy. It’s a simple contraption, free of wires and operating only with the help of reactive coatings. To convert energy from sunlight into chemical energy, the leaf splits water molecules into its component hydrogen and oxygen parts through the photosynthetic process.

This model is more practical than past efforts, which relied upon costly elements like platinum for manufacturing. It utilizes cheap, earth-abundant materials like cobalt and a nickel-molybdenum-zinc compound to do work its photosynthetic magic. A sunlight collector is sandwiched between the two film layers, which, when dropped into a jar of water exposed to sunlight, begins to bubble like a tablet of alka-seltzer. One side of the leaf produces hydrogen, the other, oxygen. The hydrogen bubbles, if captured, can be used in fuel cells to make electricity.

“You can use it under very, very simple engineered conditions,” Nocera said. “It lends itself to being highly distributed because of its simplicity.”

Nocera has big plans for his leaf. Because it’s easy to manufacture and doesn’t require a large infrastructure, he sees it as a means for producing energy for the billions of people living in the developing world. He can also envision uses for it in the remote wilderness; for example, if soldiers were dropped off in a rural area and needed to make their own fuel. For the developed world, there would be potential marketing possibilities to people wanting to live in a self-sustaining way and get off the grid. Practically, however, it might be more difficult for someone in North America to unplug than someone in, say, Sudan, since U.S. amenities are so closely tied to existing infrastructure. “That’s why people in the developing world could adopt this technology easier than in the developed world,” Nocera said. “That’s always the problem with renewables.”

The leaf requires complementary technology in hydrogen capture and usage.

Nocera says that the leaf needs to be improved and refined before it can make a positive impact in the developing world. First, nanotechnology may make it even more efficient. Rather than needing big panel hydrogen-yielding leaves, millions of microscopic nano leaf particles could be sprinkled into a smaller container of water to produce the same effect. This would save on space and manufacturing costs. “When you get into nano, there is a potential for big cost reductions,” he said. Secondly, Nocera imagines coating the edges of plastic with the reactive layers. The plastic would collect light and feed it to the photosynthenthetic periphery. This same principle could be applied to other materials, or to nanorods. “The thing I like about it a lot is that the simplicity and the architectural design of it makes itself really adaptable to lots of new avenues of exploration,” he said.

This vision, however, cannot be realized without complementary technology in hydrogen capture and usage. “At the end of the day, you’d need to take hydrogen into an existing infrastructure,” Nocera said. Fuel cells could be one option, but they are expensive. Or burning hydrogen in an engine or a turbine could potentially work, too. Unfortunately, those capabilities have not been developed yet, though companies and labs around the world, including Nocera’s, are working on it. He predicts the necessary innovation could arrive in about five years. “The downfall of a hydrogen-based economy is that it confronts that challenge,” he said.

“We’ve done the front end, and my greatest hope is that someone will come up with the way to capture hydrogen for fuel,” Nocera said. “If anyone came on board with the technology I could adopt it immediately.”

Top image: MIT professor Daniel Nocera has developed an artificial leaf chip that can split water molecules using light. Photo by Dominick Reuter